BACKGROUND
[0001] The embodiment relates to a wireless power transmission technology. More particularly,
the disclosure relates to a method of controlling transmission power depending on
the coupling states between a wireless power transmitter and a wireless power receiver
to maximize the power transmission efficiency.
[0002] A wireless power transmission or a wireless energy transfer refers to a technology
of wirelessly transferring electric energy to desired devices. In the 1800's, an electric
motor or a transformer employing the principle of electromagnetic induction has been
extensively used and then a method for transmitting electrical energy by irradiating
electromagnetic waves, such as radio waves or lasers, has been suggested. Actually,
electrical toothbrushes or electrical razors, which are frequently used in daily life,
are charged based on the principle of electromagnetic induction. The electromagnetic
induction refers to a phenomenon in which voltage is induced so that current flows
when a magnetic field is varied around a conductor. Although the commercialization
of the electromagnetic induction technology has been rapidly progressed around small-size
devices, the power transmission distance thereof is short.
[0003] Until now, wireless energy transmission schemes include a remote telecommunication
technology based on magnetic resonance and a short wave radio frequency in addition
to the electromagnetic induction.
[0004] Recently, among wireless power transmitting technologies, an energy transmitting
scheme employing resonance has been widely used.
[0005] However, according to the energy transmitting scheme employing resonance according
to the related art, the power transmission efficiency may be varied depending on the
coupling states between the wireless power transmitter and the wireless power receiver.
[0006] Therefore, a scheme of maximizing the power transmission efficiency by reflecting
the coupling state between the wireless power transmitter and the wireless power receiver
is required.
SUMMARY
[0007] The embodiment provides a method of maximizing the power transmission efficiency
depending on the coupling state between a wireless power transmitter and a wireless
power receiver.
[0008] The embodiment provides a method of controlling the transmission power depending
on a coupling coefficient between a wireless power transmitter and a wireless power
receiver by detecting the coupling coefficient between the wireless power transmitter
and the wireless power receiver.
[0009] According to one embodiment, there is provided a wireless power transmitter to transmit
power to a load through a wireless power receiver. The wireless power transmitter
includes a power supply unit to supply AC power to the wireless power transmitter,
and a transmission coil to transmit the AC power to a reception coil of a wireless
power receiver by resonance. The wireless power transmitter controls transmission
power to be transmitted to the wireless power receiver based on a coupling state between
the transmission coil and the reception coil.
[0010] According to one embodiment, a method of controlling power of a wireless power transmitter
to transmit the power to a load through a wireless power receiver includes detecting
a coupling state between the wireless power transmitter and the wireless power receiver,
adjusting transmission power based on the coupling state, and transmitting the adjusted
transmission power to the load by resonance.
[0011] As described above, there can be provided a method of maximizing the power transmission
efficiency by controlling transmission power according to the coupling state between
the wireless power transmitter and the wireless power receiver.
[0012] According to the embodiment, the coupling coefficient between the wireless power
transmitter and the wireless power receiver is detected and the optimal reception
power is determined based on the coupling coefficient. The power transmission efficiency
can be maximized by controlling the transmission power according to the determined
reception power.
[0013] Meanwhile, any other various effects will be directly and implicitly described below
in the description of the embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014]
FIG. 1 is a block diagram showing the structure of a wireless power transmission system
according to one embodiment.
FIG. 2 is an equivalent circuit diagram showing the wireless power transmission system
according to one embodiment.
FIG. 3 is a flowchart to explain a method of controlling power according to one embodiment.
FIG. 4 is a graph showing the relation between a coupling coefficient and a load impedance
in order to satisfy the maximum power transmission efficiency.
FIG. 5 is a graph showing an example of the relation between the coupling coefficient
and the load impedance in order to satisfy the maximum power transmission efficiency
when a load is a battery.
FIG. 6 is a graph showing relation between current and voltage applied to a battery
when a load is the battery.
FIG. 7 is a graph showing the relation between the quantity of power applied to a
battery and load impedance when the load is the battery.
FIG. 8 is a graph showing the relation between the coupling coefficient and the load
in order to satisfy the maximum power transmission efficiency when the load is the
battery.
FIG. 9 is a block diagram showing the structure of a wireless power transmission system
according to another embodiment.
FIG. 10 is a ladder diagram to explain a method of controlling power according to
another embodiment.
FIG. 11 is a flowchart to explain a method of controlling power according to another
embodiment.
FIG. 12 is a view to explain a look-up table in which a current value when a first
output voltage is applied to an AC power generating unit, a coupling coefficient,
a second output voltage, and a preferable current range correspond to each other.
FIG. 13 is a flowchart to explain a method of detecting a coupling coefficient according
to another embodiment.
FIG. 14 is a view to explain the case that a switch is open in order to change output
impedance.
FIG. 15 is a view to explain the case that the switch is shorted in order to change
the output impedance.
FIG. 16 is a flowchart to explain a method of controlling power according to still
another embodiment.
FIG. 17 is a view to explain a look-up table used in the method of controlling power
according to the embodiment of FIG. 16.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0015] Hereinafter, embodiments will be described in detail with reference to accompanying
drawings so that those skilled in the art can easily work with the embodiments.
[0016] According to the present invention, a scheme of transmitting power through electromagnetic
induction may signify a tightly coupling scheme having a relatively low Q value, and
a scheme of transmitting power through resonance may signify a loosely coupling scheme
having a relatively high Q value.
[0017] According to one embodiment, the frequency band used for power transmission in the
tightly coupling scheme may be in the range of 100 kHz to 300 kHz, and the frequency
band used for power transmission in the loosely coupling scheme may be one of 6.78
MHz and 13.56 MHz. However, the above numeric values are provided for the illustrative
purpose.
[0018] In addition, the loosely coupling scheme of transmitting power through resonance
according to the embodiment may include a directly coupling scheme and an inductively
coupling scheme.
[0019] According to the directly coupling scheme, each of a wireless power transmitter and
a wireless power receiver directly performs power transmission by using one resonant
coil. According to the inductively coupling scheme, a wireless power transmitter transmits
power to a wireless power receiver including two reception coils through two transmission
coils.
[0020] FIG. 1 is a block diagram showing the structure of a wireless power transmission
system 10 according to one embodiment, and FIG. 2 is an equivalent circuit diagram
showing the wireless power transmission system 10 according to one embodiment.
[0021] Referring to FIG. 1, the wireless power transmission system 10 may include a power
supply device 100, a wireless power transmitter 200, a wireless power receiver 300,
and a load 400.
[0022] According to one embodiment, the power supply device 100 may be provided separately
from the wireless power transmitter 200 as shown in FIG. 1 or may be included in the
wireless power transmitter 200.
[0023] Referring to FIG. 1, the power supply device 100 may include a power supply unit
110, a switch 120, a DC-DC converter 130, a power transmission state detecting unit
140, an oscillator 150, an AC power generating unit 160, a control unit 180, and a
storage unit 170.
[0024] The power supply unit 110 may supply DC power to each component of the power supply
device 100. The power supply unit 110 may be provided separately from the power supply
device 100.
[0025] According to one embodiment, the wireless power transmitter 200 may transmit power
to the wireless power receiver 300 by using resonance. The transmission coil of the
wireless power transmitter 200 may be realized based on the inductively coupling scheme
by including a transmission induction coil unit 211 and a transmission resonant coil
unit 212 to be described later, or may be realized based on the directly coupling
scheme by including only one transmission induction coil unit 211. The switch 120
may connect the power supply unit 110 with the DC-DC converter 130, or disconnect
the power supply unit 110 from the DC-DC converter 130. The switch 120 may be open
or shorted by an open signal or a short signal of the control unit 180. According
to one embodiment, the switch 120 may be open or shorted by the operation of the control
unit 180 according to the power transmission state between the wireless power transmitter
200 and the wireless power receiver 300.
[0026] The DC-DC converter 130 may convert DC voltage, which is received from the power
supply unit 110, into DC voltage having a predetermined voltage value to be output.
[0027] After converting the DC voltage received from the power supply unit 110 into AC voltage,
the DC-DC converter 130 may boost up or drop down and rectify the converted AC voltage,
and output the DC voltage having a predetermined voltage value.
[0028] The DC-DC converter 130 may include a switching regulator or a linear regulator.
[0029] The linear regulator is a converter to receive input voltage to output a required
quantity of voltage and to discharge the remaining quantity of voltage as heat.
[0030] The switching regulator is a converter capable of adjusting output voltage through
a pulse width modulation (PWM) scheme.
[0031] The power transmission state detecting unit 140 may detect the power transmission
state between the wireless power transmitter 200 and the wireless power receiver 300.
According to one embodiment, the power transmission state detecting unit 140 may detect
the coupling state between the wireless power transmitter 200 and the wireless power
receiver 300 by detecting the power transmission state. In this case, the coupling
state may represent at least one of the distance between the wireless power transmitter
200 and the wireless power receiver 300 and the positions of the wireless power transmitter
200 and the wireless power receiver 300.
[0032] According to one embodiment, the power transmission state detecting unit 140 may
detect the power transmission state based on current flowing in the power supply device
100. To this end, the power transmission state detecting unit 140 may include a current
sensor. The current sensor may measure current flowing in the power supply device
100, and may detect the coupling state between the wireless power transmitter 200
and the wireless power receiver based on the current. The coupling state may be expressed
as a coupling coefficient between the transmission resonant coil unit 212 of the wireless
power transmitter 200 and a reception resonant coil unit 311 of the wireless power
receiver 300.
[0033] According to one embodiment, the power transmission state detecting unit 140 may
measure the intensity of current flowing when the DC voltage output from the DC-DC
converter 130 is applied to the AC power generating unit 160, but the embodiment is
not limited thereto. In other words, the power transmission state detecting unit 140
may measure the intensity of current output from the AC power generating unit 160.
[0034] According to one embodiment, the power transmission state detecting unit 140 may
include a current transformer (CT). According to one embodiment, the intensity of
current applied to the AC power generating unit may be used to find the distance between
the wireless power transmitter 200 and the wireless power receiver 300. According
to one embodiment, the intensity of the current applied to the AC power generating
unit 160 may serve as an index to represent the coupling state between the wireless
power transmitter 200 and the wireless power receiver 300. The power transmission
state detecting unit 140 may transmit a signal representing the intensity of the detected
current to the control unit 180.
[0035] Although FIG. 1 shows that the power transmission state detecting unit 140 is provided
separately from the control unit 180, the power transmission state detecting unit
140 may be included in the control unit 180.
[0036] The oscillator 150 may generate an AC signal having a predetermined frequency and
apply the AC signal to the AC power generating unit 160.
[0037] The AC power generating unit 160 may generate AC power by using the DC voltage received
from the DC-DC converter 130 and the AC signal.
[0038] The AC power generating unit 160 may amplify the AC signal generated from the oscillator
150. An amount of an AC signal to be amplified may be varied depending on the intensity
of the DC voltage through the DC-DC converter 130.
[0039] According to one embodiment, the AC power generating unit 160 may include a push-pull
type dual MOSFET.
[0040] The control unit 180 may control the overall operation of the power supply device
100.
[0041] The control unit 180 may control the DC-DC converter 130 so that preset DC voltage
is applied to the AC power generating unit 160.
[0042] The control unit 180 may receive a signal, which is related to the intensity of current
flowing when the DC voltage output from the DC-DC converter 130 is applied to the
AC power generating unit 160, from the power transmission state detecting unit 140,
and adjust at least one of the DC voltage output from the DC-DC converter 130 and
the frequency of the AC signal output from the oscillator 150 by using the signal
related to the intensity of the received current.
[0043] The control unit 180 receives the signal representing the intensity of the current
applied to the AC power generating unit 160 from the power transmission state detecting
unit 140 to determine if the wireless power receiver 300 exists. In other words, the
control unit 180 may determine the existence of the wireless power receiver 300 capable
of receive power from the wireless power transmitter 200 based on the intensity of
the current applied to the AC power generating unit 160.
[0044] The control unit 180 may control the oscillator 150 to generate an AC signal having
a predetermined frequency. The predetermined frequency may refer to a resonance frequency
of the wireless power transmitter 200 and the wireless power receiver 300 when the
power transmission is performed by using resonance.
[0045] The storage unit 170 may store the intensity of the current applied to the AC power
generating unit 160, the coupling coefficient between the wireless power transmitter
200 and the wireless power receiver 300, and the DC voltage output from the DC-DC
converter 130 corresponding to each other. In other words, the storage unit 170 may
store three values in the form of a look-up table.
[0046] The control unit 180 may search for a coupling coefficient corresponding to the intensity
of the current applied to the AC power generating unit 160 and DC voltage output from
the DC-DC converter 130 in the storage unit 170, and may control the DC-DC converter
130 so that the searched DC voltage may be output.
[0047] The wireless power transmitter 200 receives AC power from the AC power generating
unit 160.
[0048] When the wireless power transmitter 200 is realized based on the inductively coupling
scheme, the wireless power transmitter 200 may include the transmission induction
coil unit 211 and the transmission resonant coil unit 212 constituting a transmission
unit 210 shown in FIG. 2 to be described later.
[0049] When the wireless power transmitter 200 is realized based on the directly coupling
scheme, the wireless power transmitter 200 may include only the transmission induction
coil unit 211 among components of the transmission unit 210 shown in FIG. 2 to be
described later.
[0050] The transmission resonant coil unit 212 may transmit the AC power received from the
transmission induction coil unit 211 to the wireless power receiver 300 by using resonance.
In this case, the wireless power receiver 300 may include the reception resonant coil
L
3 and the reception induction coil L
4 shown in FIG. 2.
[0051] Referring to FIG. 2, the wireless power transmission system 10 may include a power
supply device 100, the wireless power transmitter 200, the wireless power receiver
300, and the load 400.
[0052] The power supply device 100 includes all components described with reference to FIG.
1, and the components basically include the functions described with reference to
FIG. 1.
[0053] The wireless power transmitter 200 may include the transmission unit 210 and a detection
unit 220.
[0054] The transmission unit 210 may include the transmission induction coil unit 211 and
the transmission resonant coil unit 212.
[0055] The AC power generated from the power supply device 100 is transmitted to the wireless
power transmitter 200, and transmitted to the wireless power receiver 300 making resonance
together with the wireless power transmitter 200. The power received in the wireless
power receiver 300 is transmitted to the load 400 through a rectifying unit 320.
[0056] The load 400 may signify a rechargeable battery or other predetermined devices requiring
power. According to the embodiment, the load impedance of the load 400 may be expressed
as "RL". According to one embodiment, the load 400 may be included in the wireless
power receiver 300.
[0057] The power supply device 100 may supply AC power having a predetermined frequency
to the wireless power transmitter 200. The power supply device 100 may supply AC power
having a resonance frequency in resonance between the wireless power transmitter 200
and the wireless power receiver 300.
[0058] The transmission unit 210 may include the transmission induction coil unit 211 and
the transmission resonant coil unit 212.
[0059] The transmission induction coil unit 211 is connected to the power supply device
100, and AC current flows through the transmission induction coil unit 211 by power
received from the power supply device 100. If the AC current is flows through the
transmission induction coil unit 211, the AC current is induced even to the transmission
resonant coil unit 212 physically spaced apart from the transmission induction coil
unit 211 due to electromagnetic induction. The power induced to the transmission resonant
coil unit 212 is transmitted to the wireless power receiver 300 forming a resonant
circuit together with the wireless power transmitter 200 through the resonance.
[0060] Power can be transmitted between two LC circuits, which are impedance-matched with
each other, through resonance. Since the transmission resonant coil unit 212 is loosely
coupled with the reception resonant coil unit 311, the power transmitted through the
resonance can be farther transmitted when comparing with the power transmitted in
the case of the tightly coupling scheme through the electromagnetic induction. Accordingly,
the wireless power transmitter 200 and the wireless power receiver 300 have the higher
alignment free degree so that the wireless power transmitter 200 and the wireless
power receiver 300 transmit power with higher efficiency.
[0061] The transmission resonant coil unit 212 of the wireless power transmitter 200 may
transmit power to the reception resonant coil unit 311 of the wireless power receiver
300 through a magnetic field.
[0062] In detail, the transmission resonant coil unit 212 and the reception resonant coil
unit 311 are magnetically loosely coupled with each other.
[0063] Since the transmission resonant coil unit 212 is loosely coupled with the reception
resonant coil unit 311, the power transmission efficiency between the wireless power
transmitter 200 and the wireless power receiver 300 can be significantly improved.
[0064] The transmission induction coil unit 211 may include a transmission induction coil
L1 and a capacitor C1. In this case, the capacitance of the capacitor C1 is a value
adjusted for the operation at the resonance frequency.
[0065] One terminal of the capacitor C1 is connected to one terminal of the power supply
device 100, and an opposite terminal of the capacitor C1 is connected to one terminal
of the transmission induction coil L1. An opposite terminal of the transmission induction
coil L1 is connected to an opposite terminal of the power supply device 100.
[0066] The transmission resonant coil unit 212 includes a transmission resonant coil L2,
a capacitor C2, and a resistor R2. The transmission resonant coil L2 includes one
terminal connected to one terminal of the capacitor C2 and an opposite terminal connected
to one terminal of the resistor R2. The opposite terminal of the resistor R2 is connected
to the opposite terminal of the capacitor C2. The resistance of the resistor R2 represents
the quantity of power loss in the transmission resonant coil L2, and the capacitance
of the capacitor C2 is a value adjusted for the operation at the resonance frequency.
[0067] The detection unit 220 may detect the coupling state between the wireless power transmitter
200 and the wireless power receiver 300. According to one embodiment, the coupling
state may be detected based on the coupling coefficient between the transmission resonant
coil unit 212 and the reception resonant coil unit 311. In this case, the detection
unit 220 may detect the coupling coefficient by measuring the input impedance, and
the detail thereof will be described later.
[0068] The wireless power receiver 300 may include a reception unit 310 and a rectifying
unit 320.
[0069] The wireless power receiver 300 may be embedded in an electronic appliance such as
a cellular phone, a mouse, a laptop computer, and an MP3 player.
[0070] The reception unit 310 may include a reception resonant coil unit 311 and a reception
induction coil unit 312.
[0071] The reception resonant coil unit 311 includes a reception resonant coil L3, a capacitor
C3, and a resistor R3. The reception resonant coil L3 includes one terminal connected
to one terminal of the capacitor C3 and an opposite terminal connected to one terminal
of the resistor R3. An opposite terminal of the resistor R3 is connected to an opposite
terminal of the capacitor C3. The resistance of the resistor R3 represents the quantity
of power loss in the transmission resonant coil L3, and the capacitance of the capacitor
C3 is a value adjusted for the operation at the resonance frequency.
[0072] The reception induction coil unit 312 includes a reception induction coil L4 and
a capacitor C
4. The reception resonant coil L4 includes one terminal connected to one terminal of
the capacitor C
4. An opposite terminal of the reception induction coil L
4 is connected to an opposite terminal of the rectifying unit 320. An opposite terminal
of the capacitor C
4 is connected to one terminal of the rectifying unit 320.
[0073] The reception resonant coil unit 311 and the transmission resonant coil unit 212
maintain a resonance state at a resonance frequency. In other words, the reception
resonant coil unit 311 and the transmission resonant coil unit 212 are resonance-coupled
with each other so that AC current flows through the reception resonant coil unit
311. Accordingly, the reception resonant coil unit 311 may receive power from the
wireless power transmitter 200 through a non-radiative scheme.
[0074] The reception induction coil unit 312 receives power from the reception resonant
coil unit 311 through the electromagnetic induction, and the power received in the
reception induction coil unit 312 is rectified by the rectifying unit 320 and sent
to the load 400.
[0075] The rectifying unit 320 may receive the AC power from the reception induction coil
unit 312 and convert the received AC power into DC power.
[0076] The rectifying unit 320 may include a rectifying circuit (not shown) and a smoothing
circuit (not shown).
[0077] The rectifying circuit may include a diode and a capacitor to convert the AC power
received from the reception induction coil unit 312 to DC power and sent the DC power
to the load 400.
[0078] The smoothing circuit may smooth the rectified output. The smoothing circuit may
include a capacitor.
[0079] The load 400 may receive the DC power rectified from the rectifying unit 320.
[0080] The load 400 may be a predetermined rechargeable battery or device requiring the
DC power. For example, the load 400 may refer to a battery of a cellular phone, but
the embodiment is not limited thereto.
[0081] According to one embodiment, the load 400 may be included in the wireless power receiver
300.
[0082] A quality factor and a coupling coefficient are important in the wireless power transmission.
[0083] The quality factor may refer to an index of energy that may be stored in the vicinity
of the wireless power transmitter or the wireless power receiver.
[0084] The quality factor may be varied depending on the operating frequency ω as well as
a shape, a dimension and a material of a coil. The quality factor may be expressed
as following equation, Q= ω *L/R. In the above equation, L refers to the inductance
of a coil and R refers to resistance corresponding to the quantity of power loss caused
in the coil.
[0085] The quality factor may have a value of 0 to infinity.
[0086] The coupling coefficient represents the degree of magnetic coupling between a transmission
coil and a reception coil, and has a value in the range of 0 to 1.
[0087] The coupling coefficient may be varied depending on the relative position and distance
between the transmission coil and the reception coil.
[0088] The wireless power transmitter 200 may interchange information with the wireless
power receiver 300 through in-band communication or out-of-band communication.
[0089] The in-band communication refers to the communication for interchanging information
between the wireless power transmitter 200 and the wireless power receiver 300 through
a signal having the frequency used in the wireless power transmission. The wireless
power receiver 300 may further include a switch and may receive or may not receive
power transmitted from the wireless power transmitter 200 through a switching operation
of the switch. Accordingly, the wireless power transmitter 200 can recognize an on-signal
or an off-signal of the wireless power receiver 300 by detecting the quantity of power
consumed in the wireless power transmitter 200.
[0090] In detail, the wireless power receiver 300 may change the power consumed in the wireless
power transmitter 200 by adjusting the quantity of power absorbed in a resistor by
using the resistor and the switch. The wireless power transmitter 200 may acquire
the state information of the wireless power receiver 300 by detecting the variation
of the power consumption. The switch may be connected to the resistor in series. According
to one embodiment, the state information of the wireless power receiver 300 may include
information about the present charge quantity and the change of the charge quantity
in the wireless power receiver 300.
[0091] In more detail, if the switch is open, the power absorbed in the resistor becomes
zero, and the power consumed in the wireless power transmitter 200 is reduced.
[0092] If the switch is short-circuited, the power absorbed in the resistor becomes greater
than zero, and the power consumed in the wireless power transmitter 200 is increased.
If the wireless power receiver repeats the above operation, the wireless power transmitter
200 detects power consumed therein to make digital communication with the wireless
power receiver 300.
[0093] The wireless power transmitter 200 receives the state information of the wireless
power receiver 300 through the above operation so that the wireless power transmitter
200 can transmit appropriate power.
[0094] To the contrary, the wireless power transmitter 200 may include a resistor and a
switch to transmit the state information of the wireless power transmitter 200 to
the wireless power receiver 300. According to one embodiment, the state information
of the wireless power transmitter 200 may include information about the maximum quantity
of power to be supplied from the wireless power transmitter 200, the number of wireless
power receivers 300 receiving the power from the wireless power transmitter 200 and
the quantity of available power of the wireless power transmitter 200.
[0095] The out-of-band communication refers to the communication performed through a specific
frequency band other than the resonance frequency band in order to exchange information
necessary for the power transmission. The wireless power transmitter 200 and the wireless
power receiver 300 can be equipped with out-of-band communication modules to exchange
information necessary for the power transmission. The out-of-band communication module
may be installed in the power supply device. In one embodiment, the out-of-band communication
module may use a short-distance communication technology, such as Bluetooth, Zigbee,
WLAN or NFC, but the embodiment is not limited thereto.
[0096] Hereinafter, a method of controlling power according to one embodiment will be described
in detail with reference to FIGS. 3 to 8.
[0097] FIG. 3 is a flowchart to explain the method of controlling power according to one
embodiment. FIG. 4 is a graph showing the relation between a coupling coefficient
and a load impedance in order to satisfy the maximum power transmission efficiency.
FIG. 5 is a graph showing an example of the relation between the coupling coefficient
and the load impedance in order to satisfy the maximum power transmission efficiency
when a load is a battery. FIG. 6 is a graph showing relation between current and voltage
applied to a battery when a load is the battery. FIG. 7 is a graph showing the relation
between the quantity of power applied to a battery and load impedance when the load
is the battery. FIG. 8 is a graph showing the relation between the coupling coefficient
and the load in order to satisfy the maximum power transmission efficiency when the
load is the battery.
[0098] Hereinafter, the method of controlling the power will be described with reference
to FIG. 3 as well as FIGS. 1 and 2.
[0099] The wireless power transmitter 200 measures an input impedance (step S101). The input
impedance may be a first input impedance Z1. The first input impedance Z1 may be impedance
when viewed from the power supply device 100 to the wireless power transmitter 200
as shown in FIG. 2. According to one embodiment, the detection unit 220 may measure
the first input impedance Z1 by using current and voltage input to the wireless power
transmitter 200 from the power supply device 100.
[0100] Referring to FIG. 3 again, the detection unit 220 detects the coupling state between
the wireless power transmitter 200 and the wireless power receiver 300 by using the
input impedance (step S103). According to one embodiment, the coupling state between
the wireless power transmitter 200 and the wireless power receiver 300 may be detected
by measuring a coupling coefficient K2 between the transmission resonant coil L2 and
the reception resonant coil L3. In this case, the coupling coefficient K2 represents
the electromagnetic coupling degree between the transmission resonant coil L2 and
the reception resonant coil L3. The coupling coefficient K2 may be varied depending
on at least one of the distance between the wireless power transmitter 200 and the
wireless power receiver 300, and the directions and the positions of the wireless
power transmitter 200 and the wireless power receiver.
[0101] The detected coupling state may be used to control the power to be transmitted to
the wireless power receiver 300 by the wireless power transmitter 200. According to
one embodiment, the wireless power transmitter 200 may increase the quantity of the
power to be transmitted to the wireless power receiver 300 as the magnetic coupling
between the wireless power transmitter 200 and the wireless power receiver 300 is
weakened, and may decrease the quantity of the power to be transmitted to the wireless
power receiver 300 as the magnetic coupling between the wireless power receiver 200
and the wireless power receiver 300 is strengthened.
[0102] Hereinafter, the method of detecting the coupling state, particularly, the coupling
coefficient will be described.
[0103] Referring to FIG. 2, a third input impedance Z3 may refer to an impedance when viewed
from the reception resonant coil unit 311 to the reception induction coil unit 312,
and may be expressed as Equation 1.
[0104] In Equation 1, ω represents the resonance frequency when the transmission resonant
coil L2 and a reception resonant coil L3 make resonance, and M3 refers to the mutual
inductance between the reception resonant coil L3 and the reception induction coil
L4. In addition, ZL refers to an output impedance. The output impedance ZL may be
equal to the impedance RL of the load 400.
[0105] The mutual inductance M3 may be calculated through Equation 2.
[0106] In Equation 2, K
3 represents the coupling coefficient between the reception resonant coil L
3 and the reception induction coil L
4 and is a fixed value. Since the inductance of the reception resonant coil L
3 and the inductance of the reception induction coil L
4 are fixed values, the mutual inductance M
3 is a fixed value.
[0107] Since the resonance frequency ω, the mutual inductance M
3, the load impedance Z
L, the inductance of the reception induction coil L
4, and the capacitance of the capacitor C
4 are fixed values, the third input impedance Z
3 has a fixed value.
[0108] Equation 1 is expressed based on a frequency domain, and following equations are
expressed based on frequency domains.
[0109] The second input impedance Z
2 refers to an impedance when viewed from the wireless power transmitter 200 to the
wireless power receiver 300, and may be expressed as Equation 3.
[0110] In Equation 3, M
2 refers to the mutual inductance between the transmission resonant coil L
2 and the reception resonant coil L
3, and C
3 refers to a capacitor expressed when the reception resonant coil unit 311 is converted
into an equivalent circuit. In addition, R3 represents the quantity of power loss
occurring in the reception resonant coil L3 as a resistance.
[0111] The capacitance of the capacitor C
3, the inductance of the reception resonant coil L3, the third input impedance Z
3, and the resistor R
3 are fixed values.
[0112] The mutual inductance M
2 may be calculated through Equation 4.
[0113] In Equation 4, since the inductance of the transmission resonant coil L
2 and the inductance of the reception resonant coil L
3 are fixed values, the mutual inductance M
2 may be varied depending on the coupling coefficient K
2 between the transmission resonant coil L
2 and the reception resonant coil L
3.
[0114] Accordingly, if the third input impedance Z
3 in Equation 1 is substituted into Equation 3, the second input impedance Z
2 may be expressed in relation to the mutual inductance M
2, and may be varied depending on the mutual inductance M
2.
[0115] The first input impedance Z
1 refers to an impedance when viewed from the power supply device 100 to the wireless
power transmitter 200, and may be expressed as Equation 5.
[0116] In Equation 5, M
1 refers to the mutual inductance between the transmission induction coil L
1 and the transmission resonant coil L
2.
[0117] The mutual inductance M
1 may be calculated through Equation 6.
[0118] In Equation 6, since the inductance of the transmission resonant coil L
1, the inductance of the transmission induction coil L
2, and the coupling coefficient K
1 between the transmission resonant coil L
1 and the transmission induction coil L
2 are fixed values, the mutual inductance M
1 has a fixed value.
[0119] Although the inductance of the transmission induction coil L
1, the capacitance of the capacitor C
1, the mutual inductance M
1, the inductance of the transmission resonant coil L
2, the capacitor C
2, and the resistor R
2 have fixed values, the second input impedance Z
2 may be varied depending on the mutual inductance M
2.
[0120] If Equation 2 is substituted into Equation 3, the first input impedance Z
1 may be expressed in relation to the mutual inductance M
2.
[0121] The detection unit 220 may calculate the mutual inductance M
2 by using the first input impedance Z1 in the equation for the first input impedance
Z
1 measured in step S101 and the mutual inductance M
2, and may detect the coupling coefficient K
2 through the calculated mutual inductance M
2 and Equation 4.
[0122] Another scheme of detecting the coupling coefficient K
2 will be described with reference to FIG. 13.
[0123] Referring to FIG. 3 again, the wireless power transmitter 200 decides reception power
corresponding to the detected coupling state (step S105). In this case, the determined
reception power may refer to power that the load 400 must receive in order to maximize
the power transmission efficiency between the wireless power transmitter 200 and the
load 400.
[0124] Hereinafter, a scheme of detecting the coupling coefficient K
2 and deciding the reception power that the load 400 must receive depending on the
coupling coefficient K
2 will be described.
[0125] Referring to FIG. 2, the power transmission efficiency may be calculated through
following Equation 7.
[0126] In Equation 7, Pin may refer to transmission power transmitted to the wireless power
transmitter 200 by the power supply device 100, and Pout may refer to power consumed
in the load 400 and reception power received in the load 400. I
1 is current flowing through the load 400.
[0127] The current I
1 is current input to the wireless power transmitter 200 while serving as current flowing
through the transmission induction coil unit 211.
[0128] The current I
1 may be calculated through the following procedure.
[0129] When current flowing through the reception resonant coil unit 311 is represented
as I
3, the current I
3 may be expressed as following Equation 8.
[0130] When current flowing through the transmission resonant coil unit 212 is represented
as I
2, the current I
2 may be expressed as following Equation 9.
[0131] When current flowing through the transmission induction coil unit 211 is represented
as I
1, the current I
1 may be expressed as following Equation 10.
[0132] Equation 8 is substituted into Equation 9, and the substitution result of Equation
9 is substituted into Equation 10. Next, the substitution result of Equation 10 and
the first input impedance Z
1 represented as the mutual inductance M
2 are substituted in Equation 7. In this case, Equation 11 is obtained in relation
to the power transmission efficiency.
[0133] Equation 11 is arranged as Equation 12.
[0134] The quality factor Q
2 of the transmission resonant coil unit 212 is expressed as following Equation 13,
and the quality factor Q
3 of the reception resonant coil unit 311 is expressed as Equation 14.
[0135] When Equation 13 and Equation 14 are substituted into Equation 12, the substitution
result is arranged as following Equation 15.
[0136] For the calculation convenience, x is substituted as Equation 16, and m is substituted
as Equation 17.
[0137] If Equation 16 and Equation 17 are substituted into Equation 15 which is an equation
for power transmission efficiency, the power transmission efficiency may be arranged
as Equation 18.
[0138] If Equation 18 is differentiated with respect to x in order to obtain a condition
of maximizing the power transmission efficiency, following Equation 19 may be obtained.
[0139] The condition of maximizing the power transmission efficiency in Equation 19 is satisfied
when x is expressed as following Equation 20.
[0140] If x in Equation 16 and m in Equation 17 are substituted into Equation 20, following
Equation 21 is obtained.
[0141] When Equation 21 is arranged with respect to R
L, following Equation 22 is obtained.
[0142] In other words, when the impedance R
L of the load 400 has the value the same as that of Equation 22, the power transmission
efficiency is maximized. In this case, the power transmission efficiency may be calculated
as shown in FIG. 23.
[0143] In other words, when the impedance R
L of the load 400 is the same as that expressed as Equation 22, the maximum power transmission
efficiency may be obtained as Equation 23.
[0144] Referring to Equation 22, the impedance R
L of the load 400 to satisfy the condition of maximizing the power transmission efficiency
may be varied depending on the coupling coefficient K
2.
[0145] In detail, the relation between the coupling coefficient K
2 and the impedance of the load 400 is shown as a graph in FIG. 4.
[0146] In FIG. 4, an x axis represents the coupling coefficient K
2 and a y axis represents a load impedance.
[0147] Referring to FIG. 4, as the coupling coefficient K
2 is increased, the load impedance is decreased. As the coupling coefficient K
2 is decreased, the load impedance is increased. In other words, the power transmission
efficiency can be maximized when the load impedance is varied depending on the coupling
coefficient K
2. In detail, the power transmission efficiency can be maximized when the load impedance
is increased as the coupling coefficient is increased and the load impedance is increased
as the coupling coefficient is decreased.
[0148] The coupling coefficient K
2 may be varied depending on one of the distance between the wireless power transmitter
200 and the wireless power receiver 300 and positions of the wireless power transmitter
200 and the wireless power receiver 300 located in relation to each other. Accordingly,
in order to obtain the maximum power transmission efficiency, the impedance of the
load 400 may be varied.
[0149] FIG. 5 is a graph showing the relation between the coupling coefficient K and the
load impedance in detailed numeric values.
[0150] The load impedance 13.3 Ω when the coupling coefficient K
2 is 0.05, the load impedance 8 Ω when the coupling coefficient K
2 is 0.10, and the load impedance is 5 Ω when the coupling coefficient K
2 is 0.25. Accordingly, the power transmission efficiency is maximized if the load
impedance is reduced as the coupling coefficient K
2 is increased.
[0151] In general, the load 400 may include the battery of the cellular phone. The impedance
of the battery may be varied depending on the quantity of power applied to the battery.
In this case, for example, the load 400 may include the battery of the cellular phone,
but the embodiment is not limited thereto. The load 400 may include various types
of batteries if the impedance of the load 400 is varied depending on the quantity
of power applied to the load 400.
[0152] FIG. 6 is a graph showing current as a function of voltage applied to the battery.
[0153] The impedance RL of the battery may be expressed as following Equation 24.
[0154] In Equation 24, V represents voltage applied to the battery, and I represents current
flowing through the battery.
[0155] If the voltage of 4 V is applied to the battery, the quantity of power applied to
the battery is 1.2 W (4V x 0.3A). In this case, the impedance of the battery becomes
13.3 Ω (4V/0.3 A).
[0156] If the voltage of 4.583 V is applied to the battery, the quantity of power applied
to the battery becomes 2.0 W (4.583V x 0.437A). In this case, the impedance of the
battery becomes about 10.5 Ω (4.458 V/0.437 A).
[0157] If the voltage of 5V is applied to the battery, the quantity of power applied to
the battery becomes 5.0 W (5V x 1.0A), and the impedance of the battery becomes 5.0
Ω (5V/1A).
[0158] In other words, as described above, the impedance of the battery may be varied depending
on the quantity of power applied to the battery.
[0159] In addition, when the relation between the load impedance and the quantity of power
applied to the battery to satisfy the maximum power transmission efficiency is represented
as a graph based on the above result, the graph is expressed as shown in FIG. 7.
[0160] In FIG. 7, an x axis represents the quantity of power applied to the battery, and
a y axis represents the impedance of the battery (load).
[0161] As shown in FIG. 7, the impedance of the battery may be varied depending on the quantity
of power applied to the battery.
[0162] In this case, when comparing FIG. 5 with FIG. 7, the graphs shown in FIGS. 5 and
7 are similar to each other. In detail, referring to FIG. 5, the impedance of the
load is decreased as the coupling coefficient K
2 is increased, and the impedance of the load is increased as the coupling coefficient
K
2 is decreased. Referring to FIG. 7, the impedance of the battery is decreased as the
quantity of power applied to the battery is increased, and the impedance of the battery
is increased as the quantity of power applied to the battery is decreased. The waveforms
of the graphs shown in FIGS. 5 and 7 are very similar to each other.
[0163] In other words, if the wireless power transmission system 10 employs the load 400
such as a battery having impedance varying depending on the quantity of power applied
to the load 400, a specific corresponding relation is established between the coupling
coefficient K
2 and the reception power of the load 400. In this case, if the transmission power
is adjusted to establish the specific corresponding relation between the coupling
coefficient K
2 and the reception power of the load 400, the condition to obtain the maximum power
transmission efficiency shown in FIG. 5 can be satisfied.
[0164] In other words, the load impedance must be adjusted in order to obtain the maximum
transmission efficiency depending on the coupling coefficient K
2. The adjustment of the load impedance is possible by controlling the quantity of
power as shown in FIG. 7. In other words, if the reception power of the battery may
be decided depending on the coupling coefficient K
2, and the transmission power is adjusted such that the battery receives the decided
reception power, the condition of maximizing the power transmission efficiency of
FIG. 5 is satisfied, so that the maximum power transmission efficiency can be obtained.
[0165] The corresponding relation may be represented as shown in the graph of FIG. 8.
[0166] Referring to FIG. 8, the reception power received in the battery as a function of
the coupling coefficient K is shown as a graph. If the quantity of power received
in the battery is 1.2 W when the coupling coefficient is 0.05, the quantity of power
received in the battery is 2.0 W when the coupling coefficient K
2 is 0.10, and the quantity of power received in the battery is 5 W when the coupling
coefficient K
2 is 0.25, the condition to obtain the maximum power transmission efficiency shown
in FIG. 5 is satisfied.
[0167] Finally, in order to obtain the maximum power transmission efficiency, the reception
power that must be sent to the load 400 must be decided depending on the coupling
coefficient K
2.
[0168] According to one embodiment, the wireless power transmitter 200 may further include
a storage unit (not shown) to store the reception power corresponding to the coupling
coefficient K
2. The wireless power transmitter 200 searches the storage unit for the reception power
corresponding to the coupling coefficient K
2 and decide the reception power.
[0169] Referring to FIG. 3, the wireless power transmitter 200 determines present reception
power received by the load 400 (step S 107). Since the wireless power receiver 300
may send the power received from the wireless power transmitter 200 to the load 400
without power loss, the power received by the wireless power receiver 300 is assumed
as being equal to the power received by the load 400.
[0170] The wireless power transmitter 200 may determine the present reception power received
by the load 400 through various schemes.
[0171] According to one embodiment, the wireless power transmitter 200 may determine the
present reception power received by the load 400 through the out-of-band communication
described in FIG. 2. In detail, the wireless power transmitter 200 requests the information
of the present reception information received by the wireless power receiver 300 through
the out-of-band communication and receives the response to the request, thereby determining
the present reception power.
[0172] According to one embodiment, the wireless power transmitter 200 may determine the
present reception power received in the load 400 by measuring the intensity of current
flowing in the wireless power transmitter 200. In this case, the wireless power transmitter
200 may include the power supply device 100 described in FIG. 1. For example, the
intensity of current flowing inside the wireless power transmitter 200 may be related
to the present reception power received by the load 400. In detail, when the distance
between the wireless power transmitter 200 and the wireless power receiver 300 is
constant, the intensity of current flowing in the wireless power transmitter 200 may
be increased as the quantity of power received by the load 400 is increased, and the
intensity of current flowing inside the wireless power transmitter 200 may be decreased
as the quantity of the power received by the load 400 is decreased.
[0173] The wireless power transmitter 200 may include a storage unit 170 to store the intensity
of current flowing inside the wireless power transmitter 200 and the power received
by the load 400 corresponding to each other. The wireless power transmitter 200 may
find the reception power corresponding to the intensity of current by searching for
the storage unit 170 and determine the present reception power received by the load
400.
[0174] Thereafter, the wireless power transmitter 200 determines if the determined reception
power is equal to the decided reception power (step S109).
[0175] If it is determined that the determined reception power is different from the decided
reception power, the wireless power transmitter 200 decides transmission power to
be transmitted to the wireless power receiver 300 (step S111). In other words, the
wireless power transmitter 200 may decide transmission power corresponding to the
decided reception power in order to obtain the maximum power transmission efficiency.
[0176] The wireless power transmitter 200 controls transmission power to be transmitted
to the wireless power receiver 300 in order to transmit the decided transmission power
to the wireless power receiver 300 (step S113). According to one embodiment, the wireless
power transmitter 200 may control the transmission power by controlling the power
supply unit 110 to supply the power to the power supply device 100, and the details
thereof will be described in detail with reference to FIGS. 9 and 10.
[0177] According to still another embodiment, the wireless power transmitter 200 may control
the transmission power by measuring the current flowing inside the wireless power
transmitter 200, and the details thereof will be described with reference to FIGS.
11 and 12.
[0178] The wireless power transmitter 200 may receive the decided transmission power from
the power supply device 100 and transmit the transmission power to the wireless power
receiver 300. Accordingly, the load 400 may receive the reception power to satisfy
the maximum power transmission efficiency from the wireless power receiver 300.
[0179] As described above, according to the embodiment, the wireless power transmitter 200
transmits the transmission power to maximize the power transmission efficiency, and
the load 400 may receive the reception power to make the power transmission efficiency
maximized, so that the power transmission efficiency can be maximized.
[0180] Hereinafter, a method of controlling power according to another embodiment will be
described with reference to FIGS. 9 and 10 by incorporating the description made with
reference to FIGS. 1 to 8. In particular, FIGS. 9 and 10 show a scheme of controlling
the transmission power in step S113 of FIG. 3.
[0181] FIG. 9 is a block diagram showing the structure of a wireless power transmission
system according to another embodiment. FIG. 10 is a ladder diagram to explain a method
of controlling power according to another embodiment.
[0182] The wireless power transmission system 20 may include a power supply device 500,
a wireless power transmitter 900, and the wireless power receiver 300.
[0183] The wireless power receiver 300 has the same components and structure as those described
with reference to FIGS. 1 to 2.
[0184] The wireless power transmitter 900 may receive DC power from the power supply device
500. In detail, the wireless power transmitter 900 transmits a voltage control signal
to the power supply device 500 to receive adjusted DC voltage.
[0185] The wireless power transmitter 900 may further include a transmission unit 910, a
power transmission state detecting unit 930, an oscillator 940, an AC power generating
unit 950, a control unit 960, a storage unit 970, and a DC cut-off unit 980.
[0186] The power transmission state detecting unit 930 may detect the power transmission
state between the wireless power transmitter 900 and the wireless power receiver 300.
According to one embodiment, the power transmission state detecting unit 930 may detect
the power transmission state based on the current flowing inside the power supply
device 100. To this end, the power transmission state detecting unit 930 may use a
current sensor. The current sensor may detect the current flowing through a circuit
and measure the intensity of the detected current when the DC voltage received from
the power supply device 500 is applied to the AC power generating unit 950. However,
a measurement point of the power transmission state detecting unit 930 is not limited
thereto, but may include an output point of the AC power generating unit 950 to be
described later.
[0187] The intensity of current flowing inside the wireless power transmitter 900 may be
varied depending on the power transmission state between the wireless power transmitter
900 and the wireless power receiver 300. Details of the power transmission state will
be described later.
[0188] According to one embodiment, the power transmission state detecting unit 930 may
include a current transformer (CT).
[0189] The oscillator 940 may generate an AC signal having a predetermined frequency. When
the transmission unit 910 to be described later transmits power to the wireless power
receiver 300 through resonance, the oscillator 940 may generate an AC signal having
a resonance frequency to allow the transmission resonant coil included in the transmission
unit 910 to operate at the resonance frequency and transmit the AC signal to the AC
power generating unit 950. The AC signal generated from the oscillator 940 is applied
to the AC power generating unit 950.
[0190] The AC power generating unit 950 may generate AC power by using DC power received
from an AC-DC converter 510 of the power supply device 500 based on the AC signal
received from the oscillator 940.
[0191] The AC power generating unit 950 may amplify the AC signal received from the oscillator
940. According to one embodiment, the amplification degree of the AC signal may be
varied depending on the intensity of the DC voltage applied to the AC power generating
unit 950.
[0192] According to one embodiment, the AC power generating unit 950 may include a push-pull
type dual MOSFET.
[0193] The control unit 960 may control the overall operation of the wireless power transmitter
900.
[0194] The control unit 960 may detect the power transmission state variation between the
wireless power transmitter 900 and the wireless power receiver 300. The control unit
960 may detect the power transmission state variation to decide the DC power to be
received from the power supply device 500, and may transmit a power control signal
to the power supply device 500 in order to receive the decided DC power through a
PLC scheme. According to one embodiment, the power transmission state may relate to
the distance between the wireless power transmitter 900 and the wireless power receiver
300 and the directions in which the wireless power transmitter 900 and the wireless
power receiver 300 are located.
[0195] According to one embodiment, the power transmission state may relate to a power reception
state of the wireless power receiver 300. For example, if power charged in the wireless
power receiver 300 is less than a reference quantity of power, the wireless power
receiver 300 may request the wireless power transmitter 900 to transmit power greater
than present power, which is being transmitted, through out-of-band communication.
However, the wireless power transmitter 900 may decide transmission power to be transmitted
to the wireless power receiver 300 corresponding to the request. The wireless power
transmitter 900 may determine the DC power to be received from the power supply device
500 corresponding to the decided transmission power, and may control the power supply
device 500 in order to receive the determined DC power. Thereafter, the wireless power
transmitter 900 may receive the decided DC power from the power supply device 500
and convert the DC power into AC power to be transmitted to the wireless power receiver
300.
[0196] The control unit 960 may detect the coupling state between the wireless power transmitter
900 and the wireless power receiver 300 by receiving the information of the power
transmission state through the power transmission state detecting unit 930. According
to one embodiment, if the power transmission state detecting unit 930 is a current
sensor, the control unit 960 may receive the intensity of current by the current sensor
and detect the distance between the wireless power transmitter 900 and the wireless
power receiver based on the intensity of the current.
[0197] The control unit 960 may decide the DC voltage to be received from the power supply
device by using the detected distance. The control unit 960 may transmit the voltage
control signal including the information of the decided DC voltage to the power supply
device 500. In this case, the voltage control signal may be transmitted between the
wireless power transmitter 900 and the power supply device 500 through the PLC scheme.
The PLC scheme is a technology of carrying data on a high frequency signal of several
hundreds kHz to several tens MHz by employing a power line to supply power as a medium.
In other words, the PLC scheme may be performed through a power line subject to a
wiring work without separately installing a dedicated communication line.
[0198] According to one embodiment; the control unit 960 may determine the distance between
the wireless power transmitter 900 and the wireless power receiver 300 based on the
intensity of current.
[0199] According to one embodiment, the control unit 960 may decide DC voltage to be received
from the power supply 500 based on the intensity of the current instead of the determined
distance.
[0200] The storage unit 970 may store the intensity of current measured by the current sensor
of the power transmission state detecting unit 930 and the distance between the wireless
power transmitter 900 and the wireless power receiver 300 corresponding to each other
in the form of a look-up table.
[0201] The storage unit 970 may store the intensity of current measured by the current sensor
of the power transmission state detecting unit 930 and DC voltage to be received from
the power supply device 500 by the wireless power transmitter 900 corresponding to
each other in the form of a look-up table.
[0202] The storage unit 970 may store the intensity of current in the current sensor of
the power transmission state detecting unit 930, the distance between the wireless
power transmitter 900 and the wireless power receiver 300, and the DC voltage to be
received from the power supply device 500 by the wireless power transmitter 900 corresponding
to each other in the form of a look-up table.
[0203] The DC cut-off unit 980 may cut off a DC signal applied to the control unit 960.
According to one embodiment, the DC-cut off unit 980 may include a capacitor.
[0204] The transmission unit 910 may wirelessly transmit AC power output from the AC power
generating unit 950 to the wireless power receiver 300.
[0205] The power supply device 500 may include the AC-DC converter 510, the control unit
520, and the DC cut-off unit 530. According to one embodiment, the power supply device
500 may include an adaptor to convert AC power received from an external device into
DC power.
[0206] The AC-DC converter 510 may convert AC voltage received from the external device
into DC voltage having a predetermined size. In this case, the AC voltage received
from the outside may have the intensity of 220V and the frequency of 60 Hz, but the
embodiment is not limited thereto. The control unit 520 receives the voltage control
signal from the wireless power transmitter 900 to control the AC-DC converter 510
to output the DC voltage decided by the wireless power transmitter 900. In other words,
the control unit 520 may generate a voltage control signal to control the AC-DC converter
510 so that DC voltage is output corresponding to the intensity of current measured
by the wireless power transmitter 900. In this case, the AC-DC converter 510 may convert
the AC voltage received from an outside into DC voltage having a predetermined size
by receiving a voltage control signal and output the DC voltage.
[0207] The DC cut-off unit 530 may cut off the DC signal applied to the control unit 520.
According to one embodiment, the DC cut-off unit 530 may include a capacitor.
[0208] FIG. 10 is a ladder diagram to explain a method of controlling power according to
another embodiment.
[0209] Hereinafter, the method of controlling the power according to another embodiment
will be described by incorporating the description of FIG. 9.
[0210] Referring to FIG. 10, the current sensor of the power transmission state detecting
unit 930 may measure the intensity of current flowing through inside the wireless
power transmitter 900 (step S201). The current sensor of the power transmission state
detecting unit 930 may measure the intensity of detected current by detecting the
current flowing inside the wireless power transmitter 900.
[0211] According to one embodiment, the current sensor of the power transmission state detecting
unit 930 may measure the intensity of current input into the AC power generating unit
950 shown in FIG. 9. In addition, according to another embodiment, although the current
sensor of the power transmission state detecting unit 930 may measure the intensity
of current output from the AC power generating unit 950, the embodiment is not limited
thereto. In other words, the current sensor may measure the intensity of current flowing
inside the wireless power transmitter 900.
[0212] According to one embodiment, the current sensor of the power transmission state detecting
unit 930 may include a CT. The CT may measure higher-intensity current flowing through
the circuit by lowering the higher-intensity current to lower-intensity current. In
other words, the CT may measure current flowing through the circuit by transforming
the current flowing through the circuit into current proportional to the current flowing
through the circuit. In more detail, the CT may include a primary winding, a secondary
winding, and an iron core. If the electromagnetic induction phenomenon occurs due
to magnetic flux passing through the iron core, the primary current may be transformed
into the secondary current in proportion to a CT ratio, and may measure the transformed
secondary current.
[0213] According to one embodiment, the current sensor of the power transmission state detecting
unit 930 may include one of a wound-type CT, a bar-type CT, a through-type CT, a tertiary
winding CT, and a multi-core CT.
[0214] According to one embodiment, the intensity of current measured by the current sensor
of the power transmission state detecting unit 930 may be varied depending on the
distance between the wireless power transmitter 900 and the wireless power receiver
300. In other words, the increase in the intensity of the current measured by the
current sensor of the power transmission state detecting unit 930 refers to that the
wireless power transmitter 900 is closer to the wireless power receiver. The decrease
in the intensity of the current measured by the current sensor of the power transmission
state detecting unit 930 refers to that the wireless power transmitter 900 is gradually
away from the wireless power receiver.
[0215] The distance between the wireless power transmitter 900 and the wireless power receiver
300 may refer to the distance between coils included in the device.
[0216] The control unit 960 may determine the distance between the wireless power transmitter
900 and the wireless power receiver 300 based on the intensity of the measured current
(step S203). The wireless power transmitter 900 may determine the distance between
the wireless power transmitter 900 and the wireless power receiver 300 based on the
intensity of the current measured through the control unit 960. According to one embodiment,
the storage unit 970 may store the intensity of the measured current and the distance
corresponding to each other in the form of a look-up table, and the control unit 960
may determine the distance corresponding to the intensity of the measured current
by searching for the storage unit 970.
[0217] The control unit 960 decides DC voltage to be received from the power supply device
500 based on the determined distance (step S205).
[0218] According to one embodiment, the control unit 960 may decide DC voltage to be received
from the power supply device 500 based on the intensity of the measured current instead
of the distance. In this case, the step S203 may be omitted. In other words, if the
storage unit 970 stores the intensity of the measured current and the DC voltage to
be received by the wireless power transmitter 900 corresponding to each other, the
control unit 960 may decide DC voltage to be received by the wireless power transmitter
900 corresponding to the intensity of the measured current by searching for the storage
unit 970.
[0219] According to still another embodiment, the storage unit 970 may store the intensity
of current measured by the power transmission state detecting unit 930, the distance
between the wireless power transmitter 900 and the wireless power receiver 300, and
the DC voltage to be received from the power supply device 500.
[0220] The wireless power transmitter 900 transmits the voltage control signal based on
the decided DC voltage to the power supply device 500 (step S207). According to one
embodiment, the voltage control signal may be a signal to control the power supply
device 500 so that the wireless power transmitter 900 may receive the decided DC voltage
from the power supply device 500.
[0221] According to one embodiment, the wireless power transmitter 900 may make communication
with the power supply device 500 through a PLC scheme. The wireless power transmitter
900 may transmit the voltage control signal to the power supply device 500 through
the PLC scheme. The PLC scheme is a technology of carrying data on a high frequency
signal of several hundreds kHz to several tens MHz by employing a power line to supply
power as a medium. In other words, the PLC scheme may be performed through a power
line subject to a wiring work without separately installing a dedicated communication
line.
[0222] As described above, when the voltage control signal is transmitted through the PLC
scheme according to the embodiment, an additional power line to transmit the voltage
control signal is not required, so that the cost can be saved. In other words, according
to the embodiment, since the voltage control signal is transceived by using the power
line serving as a medium to transmit power between the power supply device 500 and
the wireless power transmitter 900, an additional power line is not required.
[0223] In addition, according to the embodiment, since the DC voltage received from the
power supply device 500 may be adjusted through the PLC scheme without the DC-DC converter
to convert the DC voltage into predetermined voltage, the manufacturing cost of the
wireless power transmitter 900 may be greatly saved.
[0224] During the procedure in which the wireless power transmitter 900 transmits the voltage
control signal to the power supply device 500, the DC-cut off unit 980 may cut off
a DC signal applied to the control unit 960. The wireless power transmitter 900 receives
the DC voltage from the power supply device 500. If the DC voltage is applied to the
control unit 960, since the control unit 960 may be damaged. Accordingly, the DC-cut
off unit 980 cuts off the DC voltage to protect the control unit 960.
[0225] According to one embodiment, the DC-cut off unit 980 may include a capacitor. The
impedance of the capacitor may be expressed as Xc=1/2π fC. If the DC signal is applied
to the capacitor (frequency f=0), the impedance becomes infinite to cut off the DC
signal.
[0226] Since the voltage control signal transmitted to the power supply device 500 by the
wireless power transmitter 900 is an AC signal, the control unit 960 may transmit
the voltage control signal to the power supply device 500 regardless of the DC-cut
off unit 980.
[0227] The power supply device 500 receives the voltage control signal from the wireless
power transmitter 900 and generates a voltage control signal to output DC voltage
to be transmitted to the wireless power transmitter 900 according to the received
voltage control signal (step S209). The power supply device 500 may generate the voltage
control signal to output the DC voltage to be transmitted to the wireless power transmitter
900 through the control unit 520. The control unit 520 may transmit the voltage control
signal to the AC-DC converter 510.
[0228] During the procedure in which the power supply device 500 receives the voltage control
signal from the wireless power transmitter 900, the DC-cut off unit 530 of the power
supply device 500 may cut off a DC signal applied to the control unit 960. The AC-DC
converter 510 of the power supply device 500 transmits the DC voltage to the wireless
power transmitter 900. If the DC voltage is applied to the control unit 520, the control
unit 520 may be damaged. Accordingly, the DC cut-off unit 530 may cut of the DC voltage
to protect the control unit 520.
[0229] According to one embodiment, the DC-cut off unit 530 may include a capacitor. The
impedance of the capacitor may be expressed as Xc=1/2π fC. If the DC signal is applied
to the capacitor (frequency f=0), the impedance becomes infinite to cut off the DC
signal.
[0230] The power supply device 500 adjusts the DC voltage by receiving the voltage control
signal from the control unit 520 (step S211). The power supply device 500 may adjust
the DC voltage to be transmitted to the wireless power transmitter 200 by receiving
the voltage control signal through the AC-DC converter 510. The AC-DC converter 510
may convert the AC voltage, which is applied from an outside, into predetermined DC
voltage based on the voltage control signal and output the AC voltage.
[0231] The power supply device 500 transmits the adjusted DC voltage to the wireless power
transmitter 200 (step S213). The power supply device 500 may transmit the DC voltage
adjusted through the AC-DC converter 510 to the wireless power transmitter 900.
[0232] The AC power generating unit 950 converts the received DC power into DC power based
on an AC signal having a predetermined frequency received from the oscillator 940
(step S215).
[0233] The AC power generating unit 950 transmits the output AC power to the transmission
unit 910 (step S217).
[0234] The AC power received in the transmission unit 910 may be transmitted to the wireless
power receiver 300 by resonance.
[0235] Since the power supplied from the power supply device may be controlled depending
on power transmission environments between the wireless power transmitter and the
wireless power receiver according to the embodiment as described above, an additional
DC-DC converter is not required. Accordingly, the manufacturing cost of the wireless
power transmitter can be significantly saved.
[0236] Hereinafter, a method of controlling power according to another embodiment will be
described with reference to FIGS. 11 and 12 by incorporating the description made
with reference to FIGS. 1 to 8. In particular, FIGS. 11 and 12 show a scheme of controlling
the transmission power in step S113 of FIG. 3.
[0237] FIG. 11 is a flowchart to explain a method of controlling power according to another
embodiment. FIG. 12 is a view to explain a look-up table in which a current value
when a first output voltage is applied to an AC power generating unit, a coupling
coefficient, a second output voltage, and a preferable current range correspond to
each other.
[0238] The description of the wireless power transmitter 200 is the same as that of FIG.
1. In this case, the wireless power transmitter 200 may include all components of
the power supply device 100.
[0239] First, the control unit 180 controls the DC-DC converter 130 so that the voltage
applied to the AC power generating unit 160 is adjusted to a first output voltage
(step S301). In this case, the first output voltage may refer to preset DC voltage.
[0240] Thereafter, the current sensor of the power transmission state detecting unit 140
may measure the intensity of current applied to the AC power generating unit 160 when
the DC voltage output from the DC-DC converter 130 is applied to the AC power generating
unit 160 (step S303). The intensity of the current applied to the AC power generating
unit 160 may be varied depending on the power transmission state between the wireless
power transmitter 200 and the wireless power receiver 300. According to one embodiment,
the power transmission state may refer to the distance between the wireless power
transmitter 200 and the wireless power receiver 300, and the directions of the wireless
power transmitter 200 and the wireless power receiver 300. In other words, the power
transmission state may refer to the coupling state between the wireless power transmitter
200 and the wireless power receiver 300.
[0241] According to the present invention, the coupling state may be collectively referred
to as an index related to the coupling coefficient between a transmission coil and
a reception coil due to the distance between the wireless power transmitter 200 and
the wireless power receiver 300 and the position relation between the wireless power
transmitter 200 and the wireless power receiver 300. In other words, the coupling
state according to the present invention may be collectively referred to as all indexes
related to a coupling coefficient such as the quantity of current flowing through
the wireless power transmitter 200 and the input impedance of the wireless power transmitter
200.
[0242] According to one embodiment, the power transmission state may refer to information
of the power reception state of the wireless power receiver 300.
[0243] In addition, the intensity of current applied to the AC power generating unit 160
may be related to the coupling coefficient between the transmission resonant coil
unit 212 of the wireless power transmitter 200 and the reception resonant coil unit
311. The coupling coefficient refers to the degree of the electromagnetic coupling
between the transmission resonant coil unit 212 and the reception resonant coil unit
311, and has the range of 0 to 1.
[0244] Meanwhile, the control unit 180 determines if the intensity of the measured current
is equal to or greater than a threshold value (step S305). According to one embodiment,
the threshold value may be 100 mA for the illustrative purpose. The threshold value
may refer to the minimum current value required to detect the wireless power receiver
300. In other words, if the intensity of the measured current is equal to or greater
than the threshold value, the wireless power receiver 300 is regarded as being detected.
If the intensity of the measured current is less than the threshold value, the wireless
power receiver 300 is regarded as not being detected.
[0245] If the intensity of the measured current is equal to or greater than the threshold
value, the control unit 180 decides second output voltage corresponding to the intensity
of the measured current (step S307). The control unit 180 may determine the second
output voltage by searching for the DC voltage corresponding to the intensity of current
applied to the AC power generating unit 160 in the storage unit 170. According to
one embodiment, the second output voltage may refer to voltage required to transmit
power to the wireless power receiver 300.
[0246] Thereafter, the control unit 180 controls the DC-DC converter 130 to apply the decided
second output voltage to the AC power generating unit 160 (step S309). The DC-DC converter
130 outputs the second output voltage under the control of the control unit 180 and
transmits the second output voltage to the AC power generating unit 160.
[0247] Thereafter, the current sensor 270 measures the intensity of current applied to the
AC power generating unit 160 again (step S311).
[0248] Thereafter, the control unit 180 may determine if the intensity of the measured current
is in a preferable current range (step S313). In this case, the preferable current
range may refer to a current range corresponding to the second output voltage when
the second output voltage is applied to the AC power generating unit 160. The preferable
current range may be increased as the second output voltage is increased. As the second
output voltage is decreased, the range of the second output voltage may be decreased.
[0249] The control unit 180 may search the storage unit 170 for the preferable current range
corresponding to the second output voltage, and may determine if the intensity of
the measured current is in the preferable current range.
[0250] If the intensity of the measured current is in the preferably current range, the
control unit 180 stands by for a predetermined time (step S315) and returns to step
S311. In other words, the control unit 180 may measure the intensity of current applied
to the AC power generating unit 160 and periodically determine if the intensity of
the measured current corresponds to the second output voltage applied to the AC power
generating unit 160.
[0251] Meanwhile, if the intensity of the current measured in step S105 is less than the
threshold value, the control unit 180 controls the DC-DC converter 130 to adjust the
first output voltage to 0V (step S317).
[0252] In other words, if the intensity of the measured current is less than the threshold
value, the control unit 180 determines that the wireless power receiver 300 is not
detected and thus adjusts the first output voltage to 0V. If the voltage applied to
the AC power generating unit 160 is 0V, the wireless power transmitter 200 does not
transmit power to the wireless power receiver 300.
[0253] Therefore, if the wireless power receiver 300 is not detected, the wireless power
transmitter 200 can prevent meaningless power loss.
[0254] Meanwhile, if the first output voltage is adjusted to 0V, the control unit 180 stands
by for 0.1 second (step S319). In this case, 0.1 second is provided for the illustrative
purpose.
[0255] If 0.1 second elapses, the control unit 180 returns to step S301 so that the DC voltage
applied to the AC power generating unit 160 is adjusted to the first output voltage.
[0256] Meanwhile, if the intensity of current measured in step S313 is not in the preferable
current range, the control unit 180 returns to step S307. In other words, the control
unit 180 may control the DC-DC converter 130 such that the second output voltage corresponding
to the intensity of the current measured in step S113 is applied to the AC power generating
unit 160. The intensity of the current measured in step S313 may refer to the power
reception state of the wireless power receiver 300.
[0257] For example, if the intensity of the current measured in step S313 is measured less
than the preferable current range, the distance between the wireless power transmitter
200 and the wireless power receiver 300 may be regarded as being shorter. Accordingly,
the control unit 180 may control the DC-DC converter 130 to apply DC voltage, which
is more reduced by one level, to the AC power generating unit 160, thereby reducing
the quantity of the transmission power transmitted to the wireless power receiver
300.
[0258] As described above, according to the method of controlling the power according to
the embodiment, the power reception state of the wireless power receiver 300 is detected
based on the intensity of current applied to the AC power generating unit 160 and
the quantity of the transmission power may be more adjusted in order to transmit the
power corresponding to the power reception state. Accordingly, the power transmission
efficiency can be maximized and the quantity of the power loss can be reduced.
[0259] FIG. 12 is a view to explain a look-up table in which a current value measured when
a first output voltage is applied to an AC power generating unit, a coupling coefficient,
a second output voltage, and a preferable current range correspond to each other.
[0260] The look-up table of FIG. 12 is stored in the storage unit 17.
[0261] If current measured by the power transmission state detecting unit 140 is equal to
or greater than 100 mA when the first output voltage is applied to the AC power generating
unit 160, the wireless power receiver 300 is regarded as being detected.
[0262] The first output voltage may be 12V for the illustrative purpose.
[0263] If the current measured by the power transmission state detecting unit 140 is equal
to or greater than 120 mA when the first output voltage is applied to the AC power
generating unit 160, the coupling coefficient of the transmission resonant coil unit
212 of the wireless power transmitter 200 and the reception resonant coil unit 311
of the wireless power receiver 300 correspond to 0.05. In this case, the control unit
180 determines the wireless power receiver 300 as being away from the wireless power
transmitter 200, and controls the DC-DC converter 130 so that the DC voltage applied
to the AC power generating unit 160 becomes 28V (second output voltage).
[0264] Thereafter, when the DC voltage applied to the AC power generating unit 160 is maintained
to 28V, the control unit 180 determines if the current applied to the AC power generating
unit 160 satisfies the condition of the preferable current range of 751 mA to 800
mA.
[0265] If the current applied to the AC power generating unit 160 is beyond the preferable
current range, the first output voltage (12 V) is applied to the AC power generating
unit 160 for the measurement of current. If the value of the measured current is 180
mA, the control unit 180 determines the wireless power transmitter 200 as being closer
to the wireless power receiver 300 when comparing with the case that the value of
the measured current is 120 mA.
[0266] Although the distance between the wireless power transmitter 200 and the wireless
power receiver 300 has been described in relation to the intensity of current in the
above example, various power transmission states such as the directions in which the
wireless power transmitter 200 and the wireless power receiver 300 are located may
be considered.
[0267] As described above, the wireless power transmitter 200 adjusts the power transmitted
to the wireless power receiver 300 by taking into consideration various power transmission
states such as the distance from the wireless power receiver 300 and the direction
in relation to the wireless power receiver 300 , thereby maximizing the power transmission
efficiency and preventing power loss.
[0268] Hereinafter, a scheme of detecting a coupling coefficient according to another embodiment
will be described with reference to FIGS. 13 to 15 will be described by incorporating
the description made with reference to FIGS. 1 to 3.
[0269] FIG. 13 is a flowchart to explain the scheme of detecting a coupling coefficient
according to another embodiment. FIG. 14 is a view to explain the case that a switch
SW is open in order to change output impedance Z
L. FIG. 15 is a view to explain the case that the switch SW is shorted in order to
change the output impedance Z
L.
[0270] Hereinafter, a scheme of detecting a coupling coefficient according to another embodiment
will be described with reference to FIG. 13.
[0271] First, the wireless power receiver 300 changes an output impedance (step S401). The
output impedance Z
L may refer to an impedance measured when viewed the load 400 from the reception unit
310. The wireless power receiver 300 may include the switch SW, and may change the
output impedance through the switch SW. One terminal of the switch SW is connected
to a capacitor C
4, and an opposite terminal of the switch SW is connected to one terminal of the load
400. An opposite terminal of the capacitor C
4 is connected to the one terminal of the load 400.
[0272] Referring to FIG. 14, the wireless power receiver 300 transmits an open signal to
the switch SW to open the switch SW. If the switch SW is open, the output impedance
Z
L may be expresses as Equation 25.
[0273] If resistors R
2 and R
3 are decided to 0 Ω on the assumption that the resistors R
2 and R
3 have very small values in Equation 1, Equation 3, and Equation 5, and the values
of the transmission induction coil L
1 and the capacitor C
1, the transmission resonant coil L
2 and the capacitor C
2, the reception resonant coil L
3 and capacitor C
3, and the reception induction coil L
4 and the capacitor C
4 are set in such a manner that all of the above coils and the capacitors make resonance
at the resonance frequency ω, the first input impedance Z1 in Equation 5 may be arranged
as Equation 26.
[0274] Equation 26 may be arranged as following Equation 27 by using Equation 2, Equation
4, and Equation 6.
[0275] If the values of the reception induction coil L
4 and the capacitor C
4 are decided so that the reception induction coil L
4 and the capacitor C
4 make resonance at the resonance frequency ω, and the output impedance Z
L is substituted into Equation 27, the first input impedance Z
1 is arranged as following Equation 28.
[0276] Referring to FIG. 15, the wireless power receiver 300 shorts the switch SW by transmitting
a short signal. If the switch SW is shorted, the output impedance Z
L becomes 0, and the first input impedance Z
1 is arranged as Equation 29.
[0277] The wireless power receiver 300 may short the switch SW for a predetermined time
at a predetermined period by applying the control signal to the switch SW. The period
may be 1 second, and the predetermined time may be 100 us for the illustrative purpose.
[0278] Thereafter, the detection unit 220 measures the input impedance (Step S403). According
to one embodiment, the detection unit 220 may measure the first input impedance Z
1 by using current and voltage input to the wireless power transmitter 220 from the
power supply device 100.
[0279] Thereafter, the detection unit 220 may detect the coupling coefficient between the
transmission resonant coil L
2 of the transmission unit 210 and the reception resonant coil L
3 of the reception unit 310 by using the measured input impedance (step S405). In other
words, referring to Equation 29 and Equation 30, since all variables other than the
coupling coefficient K
2 have fixed values, the coupling coefficient K2 may be detected if the first input
impedance Z
1 is measured.
[0280] Hereinafter, a method of controlling power according to still another embodiment
will be described with reference to FIGS. 16 to 17.
[0281] FIG. 16 is a flowchart to explain the method of controlling power according to still
another embodiment. FIG. 17 is a view to explain a look-up table used in the method
of controlling power according to the embodiment of FIG. 16.
[0282] Referring to FIG. 16, the wireless power transmitter 200 measures the input impedance
(step S501).
[0283] The detection unit 220 detects the coupling coefficient between the transmission
resonant coil unit 212 and the reception resonant coil unit 311 by using the measured
input impedance (step S503). Since the scheme of detecting the coupling coefficient
is the same as that described with reference to FIGS. 3 and 13, the details of the
scheme of detecting the coupling coefficient is omitted.
[0284] The wireless power transmitter 200 searches for transmission power corresponding
to the detected coupling coefficient (step S505). The storage unit 170 of the wireless
power transmitter 200 stores transmission power according to the coupling coefficient
in correspondence to the coupling coefficient in the form of a look-up table. The
wireless power transmitter 200 searches the storage unit 170 for the transmission
power corresponding to the detected coupling coefficient.
[0285] The look-up table will be described with reference to FIG. 17.
[0286] Referring to FIG. 17, a look-up table in which a distance, input test current, a
coupling coefficient, load impedance, reception power, power transmission efficiency
and transmission power correspond to each other can be shown.
[0287] In this case, the distance may refer to the distance between the wireless power transmitter
200 and the wireless power receiver 300. In detail, the distance between the wireless
power transmitter 200 and the wireless power receiver 300 may be the distance between
the transmission resonant coil unit 212 and the reception resonant coil unit 311 shown
in FIG. 2. Referring to FIG. 17, as the distance between the wireless power transmitter
200 and the wireless power receiver 300 is longer, the coupling coefficient may be
reduced.
[0288] The input test current is current applied to the wireless power transmitter 200.
[0289] The power transmission efficiency may refer to the power transmission efficiency
between the wireless power transmitter 200 and the wireless power receiver 300, or
the power transmission efficiency between the wireless power transmitter 200 and the
load 400.
[0290] The load impedance may refer to impedance of the load 400 to obtain the maximum power
transmission efficiency. It may be recognized that the relation between the load impedance
and the coupling coefficient is the same as the characteristic of the graph shown
in FIG. 4.
[0291] The reception power is power received by the load 400. The reception power represents
power that the load 400 must receive in order to obtain the maximum power transmission
efficiency.
[0292] The transmission power is power that must be transmitted from the wireless power
transmitter 200 to the wireless power receiver 300 in order to obtain the maximum
power transmission efficiency.
[0293] The wireless power transmitter 200 may search the look-up table for the transmission
power corresponding to the detected coupling coefficient.
[0294] The wireless power transmitter 200 may decide the transmission power obtained through
the search as the transmission power to be transmitted to the load 400 (step S507).
In other words, the wireless power transmitter 200 may decide the transmission power
corresponding to the detected coupling coefficient to obtain the maximum power transmission
efficiency.
[0295] The wireless power transmitter 200 controls the transmission power in order to transmit
the decided transmission power to the load 400 (step S509). According to one embodiment,
the wireless power transmitter 200 may use a scheme of controlling the transmission
power by controlling the power supply device 500 that supplies power to the power
supply device 100, and the details thereof has been described with reference to FIGS.
9 and 10.
[0296] According to still another embodiment, the wireless power transmitter 200 may control
the transmission power by measuring current flowing inside the wireless power transmitter
20, and the details thereof have been described with reference to FIGS. 11 and 12.
[0297] According to a scheme of controlling power of still another embodiment, since the
transmission power can be determined through the detection of the coupling coefficient
and the search of the storage unit, the configuration of components is simple, and
the procedure of controlling power is simple.
[0298] The method of controlling power according to the embodiment may be realized in the
form of a program executed in a computer and stored in a computer-readable medium.
The computer-readable recording medium includes a ROM, a RAM, a CD-ROM, a magnetic
tape, a floppy disk, and an optical data storage device. Further, the computer-readable
recording medium may be implemented in the form of a carrier wave (for example, transmission
through Internet).
[0299] The computer-readable recording medium may be distributed in computer systems connected
with each other through a network and a code which is readable by a computer in a
distribution scheme may be stored and executed in the computer-readable recording
medium. A functional program, a code and code segments for implementing the method
may be easily deduced by programmers skilled in the related art.